Oral bacteria colonize hard and soft tissues in mouth such as gums, tongue, enamel, dentin, root cement and dental restorations. Oral bacteria residing on enamel, dentin, cement and dental restorations supra- and sub-gingival can cause demineralisation of the hard tissue and destruction of the periodontium.
Different technologies are available for detecting caries lesions. Most of these techniques involve detecting sites of demineralization that are associated with caries lesions. These technologies generally involve analyzing the degree of demineralization though any of a variety of techniques, including the use of visual and tactile methods, X-rays and electro-chemical methods, and the use of certain dyes. The degree of observable demineralization determines how advanced the caries process has already damaged a tooth.
In general, technologies for detecting caries via detecting demineralization are not able to differentiate between infected and affected tooth tissue, which can lead to over-excavation of caries lesions. Affected tooth tissues, representing non-infected but partially demineralised hard tooth tissue, is found below the layer of infected hard tooth tissue. Infected hard tooth tissue should be removed but affected hard tooth tissue should be saved for remineralisation. For example, Ansari, Beeley, Reid and Foye (Journal of Oral Rehabilitation, 1999, 26; 453-458) determined that common dyes are not caries specific because they stain demineralized organic matrix and therefore cannot differentiate between infected non-remineralizable tissue and reversibly decalcified tissue.
Moreover, all procedures which detect caries via the degree of demineralization cannot immediately indicate if the caries process is still active or arrested. To differentiate between active and arrested caries lesions a second investigation, mostly many months later, is required to observe ongoing mineral loss over time.
Demineralization of hard tooth tissue is caused by the action of caries bacteria colonizing hard tooth tissues in mouth. All procedures which detect caries via the degree of demineralization have to wait until the caries bacteria have caused a detectable degree of mineral loss. In contrast, a procedure that is able to detect the deleterious action of caries bacteria on teeth before demineralization becomes detectable would have the advantage of being able to prevent initial caries even in its earliest stage.
U.S. Pat. No. 3,332,743 describes a test solution for evaluating individual's dental caries risk in measuring the color change of diazoresorcinol in saliva samples. However, this procedure does not provide any information about the location of caries bacteria on tooth surfaces.
In other procedures, plaque collected from tooth surfaces is used to evaluate the inherent activity to metabolize, glucose, saccharose or other sugars into organic acids outside the mouth. In one aspect, acid formation is followed by pH change occurring over time by pH indicators (U.S. Pat. No. 4,359,455). In another aspect, the lactic acid formation in the plaque sample is evaluated by the use of enzymes (i.e. lactate dehydrogenase), whereby the enzymatic reaction is linked to redox dyes to generate a visual signal (DE 10108900). Although it is well-known that the caries activity in plaque differs significantly from site to site on teeth, both procedures mix plaque from several tooth surfaces to evaluate acid production in response to the presence of carbohydrates.
DE 101 08 900 (corresponding to US 2004/0141960) relates to a process for the determination of individual's caries risk in presence of carbohydrates in saliva or plaque samples. Lactate dehydrogenase, Pyruvat, sucrose and oxidized nicotinamide adenine dinucleotide (NAD) are added and the formation of reduced nicotinamide adenine dinucleotide (NADH) is detected e.g. by redox indicators like MTT using an electron carrier, i.e. PMS.
U.S. Pat. No. 4,351,899 and U.S. Pat. No. 4,254,222 refers to procedures for measuring lactic acid in biological fluids. Lactate dehydrogenase, NAD, an electron carrier and a tetrazolium dye as redox indicator is used to measure lactic acid. In case the biological fluid is saliva, an intra-oral site directed detection of caries bacteria residing on teeth/tooth surfaces is not possible.
JP 2004-113129 shows a liquid for specifying lactic acid producing region surrounding tooth surface, comprises preset amount of lactate dehydrogenase, oxidized nicotinamide adenine dinucleotide, electronic-transition agent, tetrazolium salt and water
EP 1 191 946 relates to a procedure for intra-oral directed detection of caries bacteria residing on teeth/tooth surfaces which is based on a dental impression material supplemented with lactate dehydrogenase, oxidized nicotinamide adenine dinucleotid, a redox dye, e.g. MTT and an electron carrier, e.g. PMS.
The [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]-assay (MTT-Assay) is widely known as a test for the detection of living cells. With different modifications and adjustments the test includes an incubation of cells with MTT in an aqueous solution for usually 4 to 8 hours. E.g. Schweikl and Schmalz used it to determine the “Toxicity parameters for cytotoxicity testing of dental materials in two different mammalian cell lines” (Eur J Oral Sci. 1996 June; 104(3):292-9.).
Freimoser et al. published in “The MTT-Assay Is a Fast and Reliable Method for Colorimetric Determination of Fungal Cell Densities” (Applied And Environmental Microbiology 1999 August; 65(8): 3727-3729) the use of the MTT-Assay as a colorimetric method for the determination of cell densities. The samples containing the cells to be detected are incubated for 16 hours.